This document discusses the anatomy of the smile and factors related to aesthetics. It covers: 1) The key components of the oral region that contribute to a smile, including the lips, teeth, and dark space between the teeth. 2) How factors like lip fullness, width, and curvature can impact the appearance of a smile. 3) The dynamics of a smile, from initial lip movement to full laughter where teeth are exposed and a dark space is visible. 4) The importance of establishing harmony between the components through careful treatment planning by the dentist.

1. REMOVABLE PROSTHODONTICS
SI~CTIONEDITORS
LOUIS BLATTERFEIN
ROBERT M. MORROW
S. HOWARD PAYNE
The anatomy of a smile
T. G. Matthews, D.D.S.*
Veterans Administration Hospital, Kerrville, Texas
A pleasant smile is an expression of joy, while
other smiles may be exhilarating or embarrassed,
gleeful or winsome, haughty or hateful. A smile is a
uniquely human gesture that is unlike the grimace of
lower primates. People are concerned with their
joyful smile, the way they feel about it, and its effect
on other persons. A smile, when pleasing and attrac-
tive to observers, enriches not only the one who
smiles, but those who view it.
The dentist's responsibility to preserve, create, or
enhance a pleasing smile without impairing function
is foremost in the patient's mind, since the patient
takes function for granted. The key to successful
treatment is harmony of the components of the oral
region of the face and the oral cavity. If and when
they blend into an engaging smile, the patient,
viewer, and dentist share the result.
THE ORAL REGION AND ESTHETICS
The smile expresses itself mainly in the oral region
and eyes. The oral region includes the upper and
lower lips, the corners of the mouth, and the anterior
portion of the cheeks (Fig. I). The nasolabial
grooves, if present, pass through the oral region from
the nose toward the angles of the mouth and may
extend inferiorally. The philtrum, usually present, is
a vertical depression of the upper lip extending from
the septum of the nose to the red zone?
The lips are two highly mobile fleshy folds
surrounding the orifice of the mouth. In repose their
anatomy varies. They may be full or thin, wide or
narrow, or short or long, generally in response to
genetic dicta and the form of the teeth (Fig. 2, A-F).
Thin lips are generally stretched; thinness is due to
small musculature. Externally, the lips extend from
the base of the nose above and the chin below to the
Presented at the American Prosthodontic Society, Las Vegas,
Nev.
*Chief, Dental Service
Fig. 1. The oral region. (L), the lips; (N), the nasolabial
groove; (P), the philtrum; and (R), the red zone of the
lips.
contact line and include the exposed red zone? The
red zone of the lips generally extends to form a
curved elevation and meets the skin at an obtuse
angle. There is a depression between the red zone of
the lip and the base of the nose; another similar but
greater depression is found between the lower lip and
the chin. The curvature of the lips and the concavi-
ties present in the skin are better seen in a profile
view (Fig. 3, A-F).
The inclination of the teeth may cause the lips to
be excessively prominent or recessive. In the edentu-
lous person the lips recede, increasing the promi-
nence of the nose and chin, since the interarch
distance may be reduced and the nose and chin tend
to approximate each other (Fig. 4, A and B).
In a facial view, at rest, the lips may meet in a
straight line or curve toward the corners either
upward or downward. The short upper lip often
curves upward, remains open, and generally
produces an acute angle at the corners (Fig. 2, E).
Dentists may preserve or alter the relationships of
the visible components of the oral region and the oral
cavity by changing the position of natural or artifi-
128 FEBRUARY1978 VOLUME39 NUMBER2 0022-3913/78/0239-0128500.70/0 9 1978 The C. V. Mosby Co.

2. ANATOMY OF A SMILE
Fig. 2. Facialview of lips. A, full lips; B, thin lips; C, wide lips; D, narrow lips; E,a short upper
lip; and F, a long upper lip,
cial teeth. The major challenge in establishing
esthetic excellence is to create harmony of the
components of the oral region and oral cavity.
THE SMILE
A true smile is a complex gesture. Viewed from the
facial aspect the smile begins as the corners of the
mouth extend laterally (Fig. 5). The lips may remain
in contact except with people having a short upper
lip.
As the smile expands and approaches laughter the
lips separate, the corners of the mouth curve upward,
and the teeth are exposed t~ view (Fig. 6). Some
people show only the maxillary teeth; others the
mandibular teeth. Some show both. As the angles of
the mouth extend and the lips separate, the mesial
half of the maxillary first molars and the mandibular
second premolars may be exposed. While most
people do not expose the gingival tissues, those with
a short upper lip always do, especially when smiling.
Those with hypermobile lips or massive alveolar
processes may do the same in a broad smile.
As the smile approaches a laugh the jaws separate
and a dark space develops between the maxillary
and mandibular teeth. This space is also known as
the negative space? The teeth are then silhouetted
against the dark space (Fig. 7). While individual
teeth in a complete dentition are not obvious,
missing teeth and diastemas become conspicuous by
disrupting the usually harmonious dark space. Aber-
rations in the configuration of the dark space cause a
visual impact of surprise. The exposure of gold,
fractured anterior teeth, inharmonious pontics,
maiposed and missing teeth, or the appearance of the
THE JOURNAL OF PROSTHETIC DENTISTRY 129

3. MATTHEWS
Fig. 3. Profile view of lips. A, full lips; B, thin lips; C, wide lips; D, narrow lips; E, a short
upper lip; and F, a long upper lip.
Fig. 4, A and B. Lips of an edentulous person. B, Note the increasing prominence of the nose
and chin.
tongue alter the silhouette (Fig. 8). A well-formed
dark space lends attractiveness to the smile and
enhances the appearance of the oral region.
People with dental deformities such as missing,
carious, or unsightly teeth, hideous restorations, and
misshapen dark spaces generally make every effort to
hide their embarrassment by covering the unsightly
part with the lips. These people rarely smile or laugh.
With practiced restraint, they consciously or uncon-
sciously forcibly cover the teeth with the lips, thereby
obliterating the philtrum. These are the patients
whom dentists can help. Restoring the oral region
and teeth to a pleasing appearance restores the
patient's ability to present a pleasing smile.
In profile the first manifestation of a smile is a
thinning of the lips and a distal extension of the
corners of the mouth. This continues until the
opening of the lips exposes teeth. As in the facial
view the dark space persists and the tongue may or
may not be visible (Fig. 9).
The appearance of the oral region of the face
concerns the dentist. A component may of itself be
unattractive, but the manner in which lips, teeth,
and dark space blend creates the harmony that
makes the oral region attractive. An individual tooth
may be rotated or shorter than one on the opposite
side, or it may be slightly overlapped. These minor
discrepancies lend character to the smile, relieving
the artificiality and monotony of near-perfection.
However, major disruptions of the dark space detract
from the overall impact of the smile in the adult. For
most patients the natural smile is becoming and
should be preserved. Usually the dentist may correct
a displeasing component, but both patient and
dentist must agree on what constitutes improve-
ment.
130 FEBRUARY 1978 VOLUME .'39 NUMBER 2

4. ANATOMYOFASMILE
Fig. 5. Beginning smile. The comers of the mouth are extended with the lips in contact.
Fig. 6. Expanded smile with teeth exposed.
Fig. 7. The dark space between the maxillary teeth and lower lip.
Fig. 8. The dark space between the maxillary and mandibular teeth is distorted by a
diastema.
PRETREATMENT RECORDS
Since the dentist has the obligation to preserve or
enhance the appearance of the oral region, evalua-
tion before therapy demands an accurate record of
what exists and what should be changed. All aspects
of the oral region in repose and smiling should be
recorded. A smile anatomy chart enables the dentist
to record the teeth exposed, the extent of the teeth
exposed, the curvature of the lips, the extension of
the lips, and the all-important dark space (Fig. 10).
This profile is completed during a pretreatment
interview without the patient's knowledge, because
the forced smile is an unnatural smile. This record
can be an invaluable aid, even years later, in the
creation of an attractive smile.
Full-face and profile photographs are useful.
However, posed photographs lack dynamism; the
relationships of lips, teeth, and dark space are ever-
changing.
It is a mistake to be hypercritical of each minor
imperfection. Calling the patient's attention to
minute variances only focuses attention on them.
Fig. 9. Note the dark space between maxillary and
mandibular teeth.
The patient may not have noticed a hypocalcified
area, an asymmetry, or a diastema. However, any
discrepancy mentioned by the patient, no matter
how minute, deserves your attention. By alluding to
THEJOURNALOFPROSTHETICDENTISTRy 131

5. MATTHEWS
SMILE ANATOMY CHART
NAME
I. LIPS AT REST: CIRCLE THE DIAGRAMS THAT APPLY
VERTICAL
FULL AVERAGE
HORIZONTAL ~
WIDE AVERAGE
LIP
LENGTH
c..m
LONG
AGE
THIN
NARROW
~ SHORT
II.
III.
IV.
TEETH EXPOSED. CIRCLE IF APPROPRIATE. IF NOT, DRAW A LINE OR LINES REPRESENTING LIP MOVEMENT.
MAXILLARY ONLY
TONGUE VISIBLE?
ABBERATIONS NOTED:
DIASTEMATA
ROTATED TEETH
MAXILLARY AND
MANDIBULAR
YES
FRACTURED TEETH
MAXILLARY MANDIBULAR ONLY
AND GINGIVA
NO
V. INCISAL" SILHOUETTE (FRONTAL VIEW):
CONVEX:
VI. OTHER OBSERVED CHARACTERISTICS:
CONCAVE: HORIZONTAL:
VII. PATIENT PRESENTS WITH:
NATURAL TEETH
REMOVABLE PARTIAL
VIII. PATIENT LOOKS:
PROSTHESES: FIXED PARTIAL
COMPLETE DENTURES
OLDER YOUNGER THAN STATED AGE.
Fig. 10. Smile anatomy chart.
a defect the patient is telling you that it is of
concern.
SIZE OF TEETH
Teeth exposed in Smiling are a vital part of the
anatomy of a smile. Artificial teeth should blend
with the elements of the smile. Dentists must take
into consideration the patient's age, complexion, lip
movements, anatomy of the teeth, and dark space.
Patients tend to err if given a choice in the selection
of artificial teeth. Their goal is small "pearly white"
teeth. Small white teeth are always wrong in a
complete denture for the average adult? They may
not be visible when smiling and result in an enlarged
dark space, and the silhouette effect of a dark space
bordered by light teeth is lost. If small teeth are
visible too many are exposed in an open smile (Fig.
11). Pearly white teeth clash with both the gloom of
the dark space and the complexion of the patient,
creating a garish smile. Harmony dictates that the
shading of denture teeth he consistent with the age
and coloring of the patient.
132 FEBRUARY 1978 VOLUME 39 NUMBER 2

6. ANATOMY OF A SMILE
Fig. 11. Too many small white teeth are visible.
A guide to the length of teeth in the absence of
preoperative records was established by Hurst? He
measured the length of natural anterior teeth and
correlated it with the length of the upper lip. The
data provide a helpful solution.
THE INCISAL SILHOUETTE
In the frontal view the maxillary curve of the
incisal edges is convex and the mandibular concave.
This arc produces a desirable incisal silhouette; when
reversed it is unattractive. Nothing is quite so unflat-
tering as a smile showing teeth only at the lateral
part of the frame created by the lips (Fig. 12). The
viewer expects to see teeth in the midline, and such a
grotesque dark space, minus the silhouette, jolts one's
esthetic values.
AGE
Changes of age influence the anatomy of a smile.
With age the lips become less everted and less elastic.
Older patients generally show less of the maxillary
and more of the mandibular teeth. Attrition of the
incisal edges, with the borders of the dark space less
Fig. 12. A concave incisal silhouette produces a grossly
unattractive smile.
serrated, lends harmony to the senior smile. A
prosthesis for older patients should not contain teeth
anatomically suited to a youth. Such incongruity is a
disservice to the smile of a senior person. Slight
imperfections such as evidence of mesial migration
help to cast aside the impression of youthful perfec-
tion.6
SUMMARY
The anatomy of the smile is an integral part of
dentistry. Its understanding involves close scrutiny of
all elements of the oral region. It is not enough to
establish the size of teeth based on the high and low
lip lines, size of the mouth, and a shade to blend with
the age and complexion. To create a harmonious
smile the dentist must maintain or create the normal
curvature of the lips, proper exposure of the red zone
of the lips, an undistorted philtrum, and undisturbed
nasolabial grooves. These entities, maintained in
harmony with the exposed teeth, constitute the
anatomy of a smile.
In order that patients may be served properly, the
smile must be understood, recorded, and analyzed so
THE JOURNAL OF PROSTHETIC DENTISTRY 133

7. MATTHEWS
that desirable aspects may be preserved and graceless
components returned to attractiveness.
REFERENCES
1. Shapiro, H. H.: Applied Anatomy of the Head and Neck.
Philadelphia, 1943,J. B. Lippineott Company, pp 6, 7.
2. Sicher, H.: Orban's Oral Histology and Embryology. St.
Louis, 1966, The C. V. Mosby Company, p 216.
3. Lombardi, R. E.: The principles of visual perception and
their clinical application to denture esthetics. J PROSTHET
DENT29:358, 1973.
4. Krajicek, D. D.: Dental art in prosthodonties. J PROSTHET
DENT21:122, 1969.
5. Hurst, U. U.: Vertical dimension and its correlation with lip
length and interocclusal distance. J Am Dent Assoc 64:496,
1962.
6. Frush, J. P., and Fisher, R. D.: Age factor in dentogenics. J
PROSTHETDENT7:5, 1957.
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VETERANSADMINISTRATIONHOSPITAL
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